1. Field of the Invention
The present invention relates to a novel lamp unit of a vehicular headlamp. More specifically, the present invention relates to radiating light for viewing an overhead sign above a road (referred to as an overhead sign below) using part of headlamp light.
2. Related Art
A low-beam of a headlamp of a vehicle such as an automobile is strongly suppressed such that upward diffusion light is not generated, in order to ensure that dazzling light is not radiated to drivers of preceding vehicles, pedestrians, and the like. Therefore, little light reaches an upper side of a cut-off line limiting an upper end edge.
Meanwhile, in current transportation conditions, overhead signs are used to display a branch direction of a road, a distance to a major location, and the like. The overhead signs are formed from a highly reflective material to improve visibility. However, a low-beam with good performance radiates little light above the cut-off line. Therefore, there is a risk that the overhead sign may be missed.
Headlamps such as the vehicular headlamp disclosed in Patent Document 1 have been proposed that provide desired light distribution by collecting a plurality of so-called projector type lamp units. In the lamp units, a semiconductor light-emitting element such as a light-emitting diode (referred to as an LED below) is used as a light source. The light of the semiconductor light-emitting element is condensed by a reflector and part of the condensed light is shielded in the forward direction by a shade. In addition, the condensed light, which is partially shielded, is inverted and radiated forward by a projection lens with a rearward focal point in the condensed light region.
According to the lamp unit of the vehicular headlamp disclosed in Patent Document 1, the shade is disposed generally along an optical axis of the projection lens, and an upper surface of the shade is formed as a reflective surface. Light which reaches the reflective surface from the reflector is incident to the projection lens. In this manner, efficient use of the light from the light source is achieved. Accordingly, no light passes downward from a rearward focal point of the projection lens and reaches the projection lens. Therefore, no light heads toward an upper side of the cut-off line, resulting in no light for viewing the overhead sign.
According to the lamp unit of the vehicular headlamp disclosed in Patent Document 2, the shade has a window portion that is provided below the rearward focal point of the projection lens. Direct light from the LED passes through the window portion, reaches the projection lens, and illuminates a so-called overhead zone above the cut-off line. In this manner, it is possible to view the overhead sign.
[Patent Document 1] U.S. Pat. No. 6,948,836 B2
[Patent Document 2] Japanese Patent Application Laid-Open (Kokai) No. 2005-235707